Automatic dishwashing machines, widely used in residential and commercial settings, have various dishwashing cycles, each of which is a combination of steps, such as soak, prewash, main wash, rinse, sanitize, and dry. The rinse step in a warewashing cycle uses rinse water (or aqueous rinse solution) to cause substantially complete drainage of residual detergent composition and loosened soil. Rinse aid concentrates containing a nonionic material; for example, a fatty alcohol ethoxylate, are sometimes dissolved in the rinse water (or aqueous rinse solution), particularly in institutional dishwashing machines, to minimize spotting and to promote faster drying by causing the rinse water to "sheet off" or drain from the cleaned ware, such as dishes, evenly and quickly after rinsing. See U.S. Pat. No. 4,624,713 (Morganson et al.) for a general description of the function of rinse aids.
Generally, foaming is undesirable in the rinse step of warewashing because foaming reduces the action of the rinse water and might lead to an overflow from the dishwashing machine. Therefore, low-foaming surfactants or surfactants with defoaming property are preferably used in rinse aids.
Many surfactants commonly used in rinse aids are neutral or acidic compounds. The mechanism through which a surfactant provides sheeting characteristics and faster draining of water from cleaned ware are not fully understood. However, a reduction of surface energy or interfacial tension between the liquid and the solid ware surface by the surfactants is an important factor.
Nonionic surfactants have often been used in rinse aids to improve sheeting. Morganson et al., U.S. Pat. No. 4,624,713, disclose a solid rinse aid containing a surfactant and urea. Morganson et al. found that polyoxypropylene-polyoxyethylene block copolymer comprising a center block of polyoxypropylene and having a block of polyoxyethylene to each side of the center polyoxypropylene block are useful surfactants for making their rinse aids. They also found that the "reverse PLURONIC" type surfactants having a center block of polyoxyethylene units with end blocks of polyoxypropylene units were also useful for the same purpose. The use of polyoxypropylene containing and polyoxyethylene-containing block copolymers in rinse aids is also disclosed by R. J. Ceresa in Block and Graft Copolymerization, vol. 2, pp.31-37, 98-100, 154-155, John Wiley and Sons (1976).
The washing of kitchenware and tableware, such as utensils, cups, spoons, forks, and the like, with detergents and rinse aids sometimes results in corrosion of the ware. Caravajal, U.S. Pat No. 4,908,148, discloses a liquid rinse additive composition that inhibits corrosion of glassware caused by washing with an automatic dishwashing detergent composition. Such a rinse additive composition contains a nonionic, polyoxyalkylene surfactant.
Today, many of the kitchenware and tableware, such as utensils, plates, and cups, are made of plastics such as polysulfone and polycarbonate. Under the washing conditions in a modern dishwasher, the plastic ware may undergo chemical attack by the dishwashing chemicals. See van de Brom, European Patent Application No. 90203211.9, filed on Dec. 6, 1990. Such chemical attack may result in stress cracking of the plastic ware. Stress cracks are the cracks that result when the plastic ware is exposed to chemicals (usually organic) that facilitate the release of the built-in stress (or frozen-in stress) in the plastic ware. Many conventional rinse aids have been found to contain components that are not compatible with plastic ware, i.e., they attack plastics and cause stress cracking. van de Brom discloses the use of alkyl polyglycosides (APGs) in a rinse aid that attack plastics to a lesser degree than rinse aids based on other types of nonionic surfactants. That application also discloses that a long chain ketone type anti-foam agent is preferably added to the composition while nonionic surfactants are not preferred in view of their limited compatibility towards polycarbonate.